In recent years, as an apparatus which forms an image on a paper sheet, a resin film and fabric, by using ink, a light emission type inkjet recording apparatus is in heavy usage, wherein the ink is jetted from a nozzle of a recording head, and the deposited ink is hardened by emitted light from a light emission means, resulting in a fixed image. The inkjet recording apparatus is characterized in that it can form the image on a recording medium having the low absorbability of ink. Concerning the ink, mainly used is ultraviolet ray curable ink which is readily hardened by ultraviolet ray radiation (see Patent Document 1).
On the inkjet recording apparatus, since ink has a fluid nature, while the ink deposited on the recording medium is hardened and fixed by the ultraviolet ray radiation, the diameter of the ink dots increases, and the ink dots seep out each other, or the ink penetrates the recording medium, resulting in the change of image quality. That is, after ink deposition, the increase of the ink dot diameter and seeping into the recording medium become significant, therefore, it is preferable that the interval between ink-jetting and the light radiation is shortened as much as possible. For a generally used method, the light source is disposed as close as possible to the recording head (see Patent Document 2).
Patent Document 1: U.S. Pat. No. 6,145,979
Patent Document 2: Japanese Tokkaisyo 60-132767
However, when the nozzle of the recording head is as adjacent to the light source as described above, the ultraviolet rays emitted from the light source are diffusely reflected and tend to reach the nozzle, after which the ink near a nozzle mouth starts a polymeric reaction, resulting in an increase of the ink viscosity or hardened ink.
Strictly explaining the above described diffusing reflection, when the ultraviolet rays are emitted from the light source and reach the recording medium, the ultraviolet rays are scattered due to the reflection, resulting in mixed and scattered rays, wherein the complete diffuse reflection which generates the reflected light rays of various exit angles, and nearly regular reflection which generates scattered energy distribution centering on the regular reflection light, are mixed. In general, the scattered ultraviolet rays have the maximum scattered energy in the same direction as the regular reflection of the incident rays, and the more the angle increases from the regular reflection direction, the smaller the resulting scattered energy.
That is, the ultraviolet rays diverge from the light source, and when the recording head is adjacent to the light source, the ultraviolet rays traveling directly to the recording head, as well as the ultraviolet rays reflected by a reflector and traveling to the recording head, being stray ultraviolet rays, are reflected and scattered by the recording medium, and then stray ultraviolet rays reach the nozzle of the recording head.
In this case, as the ultraviolet rays reach the nozzle of the recording head, any ink near the nozzle mouse causes a compound reaction, resulting in an increase viscosity or hardening of the ink, which generates the trouble of ink jetting, whereby ink depositing accuracy is decreased, and highly precise images are rarely formed, which is problematic.
In recent years, serial type inkjet recording apparatuses incorporate an ultraviolet ray emitting device on the carriage carrying the recording head, and resulting in the tendency for the carriage to become relatively large, since it incorporates various members, such as a sub-ink tank, and its downsizing is demanded. In order to overcome the above problems, the distance between the recording head on the carriage and the ultraviolet ray emitting device has been increased, or a light trap is installed more between them, which result in a still larger size of the carriage, which does not answer downsizing. Further in the case of a line method inkjet recording apparatus, if the distance between the recording head and the ultraviolet ray emitting device is increased, and a light trap is installed at said distance, the apparatus becomes excessively large, which of course also does not result in downsizing.